Crystal Structure of Na+, K+-ATPase in the Na+-Bound State

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Science  19 Sep 2013:
DOI: 10.1126/science.1243352

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The Na+, K+–adenosine triphosphatase (ATPase) maintains the electrochemical gradients of Na+ and K+ across the plasma membrane—a prerequisite for electrical excitability and secondary transport. Hitherto, structural information has been limited to K+-bound or ouabain-blocked forms. We present the crystal structure of a Na+-bound Na+,K+-ATPase as determined at 4.3 Å resolution. Compared with the K+-bound form, large conformational changes are observed in the α subunit, whereas the β and γ subunit structures are maintained. The locations of the three Na+ sites are indicated with the unique site III at the recently suggested IIIb, as further supported by electrophysiological studies on leak currents. Extracellular release of the third Na+ from IIIb through IIIa, followed by exchange of Na+ for K+ at sites I and II, is suggested.

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